The DVB-T2 standard describes a second generation baseline transmission system for digital terrestrial television broadcasting. The specification of the DVB-T2 standard is normalized as ETSI EN 302 755: Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2).
The DVB-T2 standard is based on a coded orthogonal frequency division multiplexing (COFDM) modulation where an error correcting code is used in conjunction with an OFDM modulation. Generally, concatenated codes are implemented in COFDM systems to ensure better error protection. The concatenated code scheme changes from one standard to another. In DVB-T2 systems the inner and outer codes are both “block codes” (LDPC+BCH). In others standards such as DVB-T and ISDB-T, the inner coder is a “convolutional code” and the outer code is a “block code” (convolutional+Reed Solomon). In both cases some interleavers are used in the chain in order to mitigate the effect of channel artifacts (e.g., frequency selective channel, co-channel interferences, CW interferences, impulsive noise and so forth).
At the receiver side, the inner decoder works in both cases described above on soft decisions, meaning that a hard decision is not made on the received data but instead a reliability of each data point is used to perform a better estimate of the original data. In typical receivers, the soft decisions are quantized on a certain number of bits. The choice of this number of bits can have a large impact on the final size and cost of the receiver, in particular because of the presence in the receiver of deinterleavers, which are memory-consuming. If the number of bits is too small the performance of the receiver will decrease, but on the contrary if the number of bits is too large the memory blocks will be oversized for a small benefit in terms of performance.